Excavating method using prestressed loop girders



1967 SANJl TACHI ETAL 3,306,049

EXCAVATING METHOD USING PRESTRESSED LOOP GIRDERS Filed Feb. 4, 3.96

FIG.I.

INVENTOR.

Unite States atet patented Feb. 28, 1967 ice 3,305,049 ETHQD USENG FREETRESSED L6G? GTRDER Sanii Tachi, 1 Z-chome, Aliabanedai, Tokyo, .iapan, and

Yoshihiro KHZEJSZEEZZ, Tokyo, .iapan; said Ktizusaita assignor to said Tacit Filed Feb. 4, 1964, Ser. 3%,437 Slaims priority, application .iapan, Feb. 4, 19-53, Ta /5,394 2 Claims. (Ci. 6141) This invention relates to an excavation method using prestressed loop girders to brace the walls of the exca vation.

In the usual methods for digging a large dimension excavation, namely when a deep pit for erecting a foundation pier of large dimension is excavated, sheet steel piles, wales and bracing members such as struts, etc. are used. The bracing members, extending across the excavation, inevitably narrow the working space and hinder the removal of excavated material, carrying-in and assembly of moulding planks and reinforcing bars, concreting, etc.

It is the main object of this invention to eliminate the above disadvantages of usual methods and to construct a foundation of large dimension efficiently and economically.

According to the present invention, such an object may be attained by using loop girders only to bear the earth pressure uniformly, without using any cross bracing members.

Other and more specific o jects, features and advantages of the invention hereof will appear from the detailed description given below in conjunction with accompanying drawings which form a part of this specification and illustrate by way of example a preferred embodiment of the invention. In the drawings:

FIG. 1 is a plan view illustrating the method using loop girder bracing for excavation work, according to the present invention, FIG. 2 is an enlarged plan view of a part of the loop girder shown in FIG. 1 and FIG. 3 is a vertical sectional view of the loop girder braced excavation shown in FIG. 1.

Referring to the drawings, and particularly to FIG. 1, sheet steel piles 3 are driven into the earth in succession and with their longitudinal edges interlinked or interconnected to form a vertically extending tube which may have a circular, oblong, or other cross section. After the earth has been excavated to a suitable depth from within the zone defined by the piles and the excavated material removed, loop girders 6 are abutted against the inside faces of piles 3. These girders 6 may be composite members formed by plural arcuate members or shaped girders interconnected by bolting to joint plates 7. Jacks 8 are inserted between girder 6 and the outer walls 3 of sheet piles 3 to impart a definite initial stress to loop girder 6 and in such a manner that every portion of each section of girder 6 will have a uniform stress applied thereto for the usual circular excavation. Wedges 9 are then inserted in the gaps between loop girder 6 and the inside walls 3 of piles 3 to maintain the relative positions of piles 3 and loop girder 6 as set by the jacks in pre-stressing loop girder 6. Jacks 8 are then removed.

Following this, the excavation is continued for a further predetermined depth and another loop girder 6 is abutted against piles 9 at the lower level, prestressed by jacks 8 and wedges 9 inserted between the piles and the loop girder. This process is repeated until loop girders are installed along the whole depth of the pit at suitable intervals. The vertically adjoining loop girders 6, 6 are preferably interconnected successively by connecting stringers, if necessary.

EXQAVATENG In this way, when the excavation has been completed to the foundation bed, a foundation footing 1 is formed, on which a pole or foundation 1 is set up to construct a foundation pier. Then piles 3 are pulled out, while the loop girders d are disconnected and removed.

For an oblong pit, oblong loop girders are used, and an initial stress which is corresponding, in principle to the stress caused by earth pressure and external force, is given to the girders by means of jacks. When the external force increases in the deep portion, it is compensated by using more loop girders 6 placed at reduced vertical intervals.

In the case of the usual methods for digging large dimension excavations, the troubles mentioned above are encountered, and often results in a part of the construction members being buried in the ground. Thus the time and cost of construction are increased and the driving of piles etc. is made more difficult, so that either well sinking methods, or the like, are adopted or the dimension of the pit is limited to a small scale.

On the contrary, according to the present invention, as described above, the external force on the piles are borne by the loop girder and no temporary bracing members, such as struts etc., are used, so that removal of excavated material and various subsequent operations following the excavation may be freely effected without any trouble. Thereby the efiiciency is increased and the expense is reduced. By working with jacks and wedges to give the loop girders a definite stress, the stresses in the loop girders are principally radial, with very few bending stresses, even if unequal external forces act thereon, so that the bearing capacity for external forces is large. Even though bending stresses may be caused in the loop girders, if these latter are connected with stringers, the stress is transmitted to upper and lower loop girders to prevent the deformation thereof. Therefore, these stringers may be provided as occasion demands.

What is claimed is:

1. A method of excavating for foundation piers and the like, comprising the steps of driving sheet steel piles, having offset inner and outer walls, to the required depth around the periphery of the excavation, with the piles having their longitudinal edges interconnected; excavating material within the pile enclosure to a predetermined depth; placing a loop girder at substantially such depth in engagement with the radially inner walls of the piles; placing jacks between the outer wall of each pile and the outer surface of the loop girder; extending the jacks to stress the loop girder uniformly along its length, with the stresses being directed primarily radially of the loop girder and in such a manner that substantially no bending stresses are exerted on the loop girder; and repeating the foregoing steps until the required depth of the excavation is attained.

2. A method of excavating, as claimed in claim 1, including the steps of, after extending the jacks to stress the loop girder, driving wedges between the inner wall of each pile and the outer surface of the loop girder; and then retracting and removing the jacks.

References Cited by the Examiner UNITED STATES PATENTS 1,398,221 11/1921 Boardman 6l41 X FOREIGN PATENTS 1,261,055 1961 France.

564,310 1932 Germany.

CHARLES E. OCONNELL, Primary Examiner.

JACOB SHAPIRO, Examiner. 

1. A METHOD OF EXCAVATING FOR FOUNDATION PIERS AND THE LIKE, COMPRISING THE STEPS OF DRIVING SHEET STEEL PILES, HAVING OFFSET INNER AND OUTER WALLS, TO THE REQUIRED DEPTH AROUND THE PERIPHERY OF THE EXCAVATION, WITH THE PILES HAVING THEIR LONGITUDINAL EDGES INTERCONNECTED; EXCAVATING MATERIAL WITHIN THE PILE ENCLOSURE TO A PREDETERMINED DEPTH; PLACING A LOOP GIRDER AT SUBSTANTIALLY SUCH DEPTH IN ENGAGEMENT WITH THE RADIALLY INNER WALLS OF THE PILES; PLACING JACKS BETWEEN THE OUTER WALL OF EACH PILE AND THE OUTER SURFACE OF THE LOOP GIRDER; EXTENDING THE JACKS 